1. Field of the Invention
Embodiments of the invention relate to the field of substrate processing using ions. More particularly, the present invention relates to a method and system for using electrodes to modify a plasma to provide ions to a substrate.
2. Discussion of Related Art
In many present day ion processing apparatus, including plasma doping (PLAD) tools and tools that employ plasma sheath modifiers the substrates are arranged close to an ion source or plasma chamber. These conventional systems are employed to perform both ion implantation as well as thin film deposition on a substrate. In such systems the propagation distance for ions extracted from an ion source may be on the order of a few centimeters or less. Accordingly, variation in plasma properties including spatial non-uniformities and time dependent variation of plasmas may strongly affect substrate processing.
In some cases, ions may be extracted in the form of a ribbon beam having a cross section that is elongated in one direction. To process substrates over a large area a ribbon beam may be scanned with respect to a substrate while an implantation process is performed. In order to process such substrates uniformly it is desirable to control spatial uniformity of ions within a ribbon beam extracted from a plasma chamber. In addition, in present day systems that employ pulsed processing in which pulses of ions are provided to a substrate, it is desirable to accurately control ion current and dose provided to a substrate. In pulse operation it has been observed that ion current persists during OFF portions of a pulse leading to greater ion dose than calculated assuming a duty cycle based upon nominal ON and OFF portions of a pulse period. Moreover, mean ion energy during OFF portions may persist such that the substrate is exposed to undesired processing such as chemical etching of physical sputtering during OFF portions. In view of the above, it will be appreciated that there is a need to develop additional control capability of ion sources including pulsed type ion processes.